The present invention is directed to ventilation of a closed environment, and more particularly, to methods and apparatus for controlling flows of air supplied to the environment and drawn from the environment to satisfy various ventilation requirements.
Ventilation of a closed environment generally is considered as a process that involves drawing air from the environment and supplying air to the environment to make up for some or all of the air drawn from the environment. For some applications, ventilation may involve a dilution process in which the air supplied to a given environment includes a mixture of outside air (e.g., fresh air obtained exterior to the environment) and recycled air (e.g., air obtained from one or more rooms in the closed environment). Accordingly, in some ventilation applications, output air which is drawn from the environment may be divided into return air which is returned to the environment at some point and exhaust air which is exhausted from the environment to the outside.
In general, a flow of air that is drawn from or supplied to a closed environment by a ventilation system may be expressed as a volume of air per unit time, for example, in terms of cubic feet per minute (cfm). Ventilation standards established by the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) provide some examples of guidelines for minimum acceptable ventilation system parameters in terms of the respective flows of air drawn from and supplied to a given environment. In particular, the ASHRAE standards establish guidelines for the flow of fresh outdoor air that should be supplied to an environment in a given time period to insure the safety and comfort of one or more persons occupying the environment from time to time.
For some ventilation applications, a variety of potentially harmful substances, or xe2x80x9ccontaminants,xe2x80x9d may be present in the environment to be ventilated. The potential presence of a variety of contaminants in an environment may in turn affect the desirability of recycling air (i.e., returning air drawn from the environment back to the environment) in the ventilation system.
One example of an environment in which a ventilation system may be employed is a laboratory. A laboratory generally is a facility that is designed to permit the safe use of various chemicals, toxic compounds and/or other potentially harmful substances for research or other purposes. The laboratory may be equipped with one or more devices or apparatus designed to exhaust air from the lab to an outside environment to protect lab users from potentially dangerous exposure to harmful substances. For example, a laboratory may include one or more exhaust devices such as laboratory fume hoods, canopy hoods, glove boxes, or biological safety cabinets, in which potentially harmful substances regularly may be handled, and/or exhaust trunks or xe2x80x9csnorkelsxe2x80x9d which may be located exterior to hoods to exhaust air from a particular area (e.g., a bench top or analytical instrument) where potentially harmful substances occasionally may be handled. Additionally, a laboratory may include one or more exhausted storage cabinets to store potentially harmful substances and contain harmful fumes or vapors possibly emanating from such substances. In each of the foregoing laboratory exhaust apparatus (hereinafter referred to collectively as xe2x80x9cauxiliary exhaust devicesxe2x80x9d), generally air is drawn from the laboratory environment and exhausted to the outside, and is not recirculated to the laboratory environment.
In view of the foregoing, conventional ventilation processes in a laboratory environment generally involve supplying 100% fresh outdoor air to the laboratory environment to make up for the air exhausted from the environment. In particular, in such processes, typically no air is recirculated from the laboratory environment back to the laboratory environment even though the air drawn from the lab environment often may be clean and safe. Furthermore, due to simplicity and costs, some portions of the lab environment served by the laboratory ventilation system, such as storage areas, office areas, xe2x80x9cdryxe2x80x9d laboratories (e.g., where generally no potentially harmful substances are handled), and the like, are also ventilated with 100% outside air, even though the possibility of contaminants being present in these areas is remote or nonexistent. Accordingly, the demand for 100% outside air in conventional laboratory ventilation systems often results in wasted resources (i.e., fresh outdoor air) and unnecessarily excessive operating costs.
With respect to ventilation systems in general, at least two guidelines may be considered in determining an appropriate flow of air supplied to (and drawn from) a given closed environment. One such guideline generally is referred to as a xe2x80x9cminimum ventilation requirement,xe2x80x9d as alluded to briefly above in connection with the ASHRAE ventilation standards. The minimum ventilation requirement relates to a volume of fresh air that should be supplied to a given closed environment (or a particular portion thereof) in a given time period to establish a minimum level of dilution ventilation in the environment. Often, the minimum ventilation requirement is expressed in terms of xe2x80x9cair changes per hourxe2x80x9d (ACH), but may be alternatively expressed in terms of an airflow in cubic feet per minute (cfm). In particular, a minimum ventilation requirement given in units of ACH may be converted to an airflow in units of cfm by multiplying the minimum ventilation requirement by the volume of the environment and dividing this product by 60 minutes per hour. For example, for an environment having a volume of 1,000 cubic feet, a minimum ventilation requirement of 6 ACH may be given in terms of airflow in cfm by the following conversion:
(6 ACHxc3x971000 cubic feet)/60 minutes per hour=100 cfm.
For purposes of the present disclosure, the term xe2x80x9cminimum ventilation requirementxe2x80x9d is used in a manner consistent with the description above.
Another guideline that may be considered in determining an appropriate flow of air supplied to (and drawn from) an environment in a ventilation system generally is referred to as a xe2x80x9cthermal load requirement.xe2x80x9d In one aspect, the thermal load requirement for a given closed environment may relate to a flow of supply air (in cfm) having a particular temperature that is required to appropriately cool (or heat) the environment (or a particular portion thereof) to a desired temperature set point. In this aspect, the thermal load requirement not only depends on the temperature of the air supplied to the environment and the desired temperature set point, but typically is also a function of a xe2x80x9cthermal loadxe2x80x9d which may be present in the environment. The term xe2x80x9cthermal loadxe2x80x9d in this aspect generally refers to anything in the space, such as instrumentation or other apparatus (e.g., lab analysis equipment, computer equipment, etc.) which may generate heat in the environment (or a particular portion thereof). Such thermal loads generally may be collectively characterized in terms of the number of Watts per square foot that all of the loads generate in the space.
In another aspect, the thermal load requirement for a given closed environment may relate to a flow of supply air (in cfm) having a particular moisture content that is required to appropriately humidify (or dehumidify) the environment (or a particular portion thereof) to a desired humidity. Based on the foregoing, it should be appreciated that more generally, the thermal load requirement may relate to a flow of supply air having a particular moisture content and/or a particular temperature so as to condition the environment in terms of one or both of temperature and humidity. For purposes of the present disclosure, the term xe2x80x9cthermal load requirementxe2x80x9d is used in a manner consistent with the foregoing description.
While a detailed explanation of the derivation of the thermal load requirement for an environment may be somewhat complicated and unnecessary for purposes of the present discussion, one useful approximation for deriving a thermal load requirement under certain conditions particularly related to temperature (as opposed to humidity) is provided here as an illustrative example. In this example, it is assumed that a heat generating thermal load of 10 Watts per square foot (e.g., expected to be generated by equipment, lights, and people) is present in a closed environment having an approximately nine foot ceiling, and that relatively cool air having a temperature of approximately 55xc2x0 F. is supplied to the environment to maintain a desired temperature set point of approximately 70xc2x0 F. Under these conditions, the environment has a thermal load requirement (in this particular case, a thermal load cooling requirement) of approximately 1.5 cubic feet per minute (cfm) of supply airflow per square foot of the environment. Accordingly, in this example, an actual thermal load requirement for the environment may be obtained by using the foregoing relationship (i.e., 1.5 cfm/ft2) and multiplying by the area of the environment in square feet to obtain the thermal load requirement in units of cfm.
In conventional ventilation systems that consider both the minimum ventilation requirement and the thermal load requirement for an environment, typically the greater of the minimum ventilation requirement and the thermal load requirement determines the flow of air supplied to the environment (and hence the flow of air drawn from the environment). In environments such as the laboratory described above, which may include one or more auxiliary exhaust devices that exhaust air from the environment to the outside, the amount of supply air required to make up for such exhaust air may in some cases satisfy (or even exceed) the greater of the minimum ventilation requirement and the thermal load requirement.
For example, laboratory exhaust hoods generally have minimum airflow requirements to exhaust potentially harmful substances that may be handled by lab personnel in the hood. In some cases, especially in lab environments with more than one auxiliary exhaust device, a sum of such minimum exhaust airflow requirements for each exhaust device may more than satisfy the greater of the minimum ventilation requirement and the thermal load requirement for the environment. Hence, in this situation, the greatest of the minimum exhaust airflow requirement from one or more auxiliary exhaust devices, the minimum ventilation requirement, and the thermal load requirement generally determines the required flow of air supplied to the environment.
In some ventilated environments, however, the thermal load requirement may be significantly greater than the minimum ventilation requirement (and the minimum exhaust airflow requirement if one or more auxiliary exhaust devices are present). This condition is in part due to the steady increase over recent years in the amount of analytical and computer equipment that is being used, for example, in various laboratories, office spaces, and the like. For example, thermal loads of 10 to 20 Watts per square foot are becoming commonplace in many ventilated environments. The result is that the thermal load requirement increasingly has become the dominant guideline that determines airflow requirements in some ventilation systems.
The trend of increased thermal load requirements for ventilated environments poses particular challenges in designing an efficient ventilation system that can be built and operated at reasonable costs. In particular, in laboratory environments in which typically no air is recirculated and 100% fresh outdoor air is supplied to the environment, increasing the thermal load requirement beyond that of either the minimum ventilation requirement or the minimum exhaust airflow requirement of any auxiliary exhaust devices present in the environment exacerbates the problem of potentially wasted resources (i.e., fresh supply air) and, hence, may lead to unnecessarily excessive operating costs.
One embodiment of the invention is directed to a method for ventilating at least a first room of a plurality of rooms in a ventilated environment, wherein the plurality of rooms are ventilated by a common source of supply air. The method comprises an act of independently satisfying a minimum ventilation requirement and a thermal load requirement for at least the first room.
In one aspect of this embodiment, the act of independently satisfying a minimum ventilation requirement and a thermal load requirement for at least the first room includes acts of drawing output air from the first room, controlling a return air flow of a first part of the output air that is returned to the ventilated environment as return air, and controlling an exhaust air flow of a second part of the output air that is exhausted from the ventilated environment as exhaust air, wherein the return air flow and the exhaust air flow are controlled such that the minimum ventilation requirement and the thermal load requirement for at least the first room are satisfied independently.
Another embodiment of the invention is directed to a computer readable medium encoded with at least one program for execution on at least one processor associated with a ventilated environment. The ventilated environment includes a plurality of rooms that are ventilated by a common source of supply air. The at least one program, when executed on the at least one processor, performs a method for ventilating at least a first room of the plurality of rooms, wherein the method comprises an act of independently satisfying a minimum ventilation requirement and a thermal load requirement for at least the first room.
Another embodiment of the invention is directed to a controller to control ventilation of at least a first room of a plurality of rooms in a ventilated environment in which the plurality of rooms are ventilated by a common source of supply air. The controller controls the ventilation of at least the first room such that a minimum ventilation requirement and a thermal load requirement for at least the first room are satisfied independently.
In one aspect of this embodiment, the ventilated environment includes at least one return air flow device that controls a return air flow of a first part of output air that is drawn from the first room and returned to the ventilated environment as return air, and at least one exhaust air flow device that controls an exhaust air flow of a second part of the output air that is drawn from the first room and exhausted from the ventilated environment as exhaust air. In this aspect, the controller controls at least the at least one return air flow device and the at least one exhaust air flow device such that the minimum ventilation requirement and the thermal load requirement for at least the first room are satisfied independently.
Another embodiment of the invention is directed to a ventilation system to ventilate at least a first room of a plurality of rooms in a ventilated environment in which the plurality of rooms are ventilated by a common source of supply air. The ventilation system comprises at least one return air flow device disposed in a path of output air drawn from the first room to vary a return air flow of at least a first portion of the output air, wherein the first portion of the output air constitutes at least a portion of return air that is returned to the ventilated environment. The ventilation system also comprises at least one exhaust air flow device in the path of the output air drawn from the first room to vary an exhaust air flow of at least a second portion of the output air, wherein the second portion of the output air is exhausted from the ventilated environment as exhaust air. The ventilation system further comprises at least one controller to control at least the at least one return air flow device and the at least one exhaust air flow device such that a minimum ventilation requirement and a thermal load requirement for at least the first room are satisfied independently.
Another embodiment of the invention is directed to a method of controlling a level of at least one contaminant present in a common source of supply air that is provided in a ventilated environment including at least a first room and a second room. The first room has drawn therefrom first return air that constitutes a first portion of air returned to the ventilated environment as at least some of the supply air. The second room has drawn therefrom second return air that constitutes a second portion of the air returned to the ventilated environment as at least some of the supply air. The method comprises an act of independently controlling at least one of a first flow of the first return air and a second flow of the second return air based at least on a detected presence of the at least one contaminant in at least one of the first room and the second room.
In one aspect of this embodiment, the act of independently controlling at least one of a first flow of the first return air and a second flow of the second return air includes acts of determining a threshold limit for the detected presence of the at least one contaminant in at least one of the first room and the second room based at least on a dilution ratio of at least one of the first flow of the first return air and the second flow of the second return air to a total uncontaminated air flow, and independently controlling at least one of the first flow of the first return air and the second flow of the second return air based at least on the threshold limit for the detected presence of the at least one contaminant.
In another aspect of this embodiment, the act of independently controlling at least one of the first flow of the first return air and the second flow of the second return air based at least on the threshold limit for the detected presence of the at least one contaminant includes an act of reducing at least one of the first flow of the first return air and the second flow of the second return air if the detected presence of the at least one contaminant in at least one of the first room and the second room exceeds the threshold limit.
In yet another aspect of this embodiment, the act of independently controlling at least one of the first flow of the first return air and the second flow of the second return air based at least on the threshold limit for the detected presence of the at least one contaminant includes an act of reducing a flow of the supply air to at least one of the first room and the second room if the detected presence of the at least one contaminant in at least one of the first room and the second room exceeds the threshold limit.
In yet another aspect of this embodiment, the act of independently controlling at least one of the first flow of the first return air and the second flow of the second return air based at least on the threshold limit for the detected presence of the at least one contaminant includes an act of increasing a flow of exhaust air that is drawn from at least one of the first room and the second room and not returned to the ventilated environment if the detected presence of the at least one contaminant in at least one of the first room and the second room exceeds the threshold limit.
Another embodiment of the invention is directed to a computer readable medium encoded with at least one program for execution on at least one processor associated with a ventilated environment including at least a first room and a second room ventilated by a common source of supply air. The first room has drawn therefrom first return air that constitutes a first portion of air returned to the ventilated environment as at least some of the supply air. The second room has drawn therefrom second return air that constitutes a second portion of the air returned to the ventilated environment as at least some of the supply air. The at least one program, when executed on the at least one processor, performs a method of controlling a level of at least one contaminant present in the supply air, wherein the method comprises an act of independently controlling at least one of a first flow of the first return air and a second flow of the second return air based at least on a detected presence of the at least one contaminant in at least one of the first room and the second room.
Another embodiment of the invention is directed to a controller to control a level of at least one contaminant present in a common source of supply air for a ventilated environment that includes at least a first room and a second room supplied by the supply air. The first room has drawn therefrom first return air that constitutes a first portion of air returned to the ventilated environment as at least some of the supply air. The second room has drawn therefrom second return air that constitutes a second portion of the air returned to the ventilated environment as at least some of the supply air. The controller independently controls at least one of a first flow of the first return air and a second flow of the second return air based at least on a detected presence of the at least one contaminant in at least one of the first room and the second room.